III-V antimonide-based detectors are under development as a possible alternative to HgCdTe material systems. Although the modern version of this technology is still in its infancy, during the last decade, antimonide-based focal plane array technology has achieved a level close to HgCdTe. This book describes current concepts of antimonide-based IR detectors, focusing on designs having the largest impact on the mainstream of IR detector technologies. It is suitable for graduate students in physics and engineering who have knowledge of modern solid-state physics and electronic circuits, and will be of interest to those working with aerospace sensors and systems, remote sensing, thermal imaging, military imaging, optical telecommunications, infrared spectroscopy, and lidar.

6.6.1 The Ndoptdiff product as the figure of merit for diffusion-limited photodetectors

6.6.2 Dark current density

6.6.3 Noise equivalent difference temperature

6.6.4 Comparison with experimental data

6.7 Multicolor Barrier Detectors

References

7 Cascade Infrared Photodetectors

7.1 Multistage Infrared Detectors

7.2 Type-II Superlattice Interband Cascade Infrared Detectors

7.2.1 Principle of operation

7.2.2 MWIR interband cascade detectors

7.2.3 LWIR interband cascade detectors

7.3 Performance Comparison with HgCdTe HOT Photodetectors

References

8 Coupling of Infrared Radiation with Detector

8.1 Standard Coupling

8.2 Plasmonic Coupling

8.2.1 Surface plasmons

8.2.2 Plasmonic coupling of infrared detectors

8.3 Photon Trapping Detectors

References

9 Focal Plane Arrays

9.1 Trends in Infrared Focal Plane Arrays

9.2 Infrared FPA Considerations

9.3 InSb Arrays

9.4 InAsSb nBn Detector FPAs

9.5 Type-II Superlattice FPAs

References

10 Final Remarks

10.1 P-on-n HgCdTe Photodiodes

10.2 Manufacturability of Focal Plane Arrays

10.3 Conclusions

References

Preface

Among the many materials investigated in the infrared (IR) field, narrow-gap
semiconductors are the most important in the IR photon detector family.
Although the first widely used narrow-gap materials were lead salts (during
the 1950s, IR detectors were built using single-element-cooled PbS and PbSe
photoconductive detectors, primarily for anti-missile seekers), this semiconductor
family was not well distinguished. This situation seems to have resulted from
two reasons: the preparation process of lead salt photoconductive polycrystalline
detectors was not well understood and could only be reproduced with
well-tried recipes; and the theory of narrow-gap semiconductor bandgap
structure was not well known for correct interpretation of the measured
transport and photoelectrical properties of these materials.

The discovery of the transistor stimulated a considerable improvement
in the growth and material purification techniques. At the same time, rapid
advances were being made in the newly discovered III-V compound
semiconductor family. One such material was InSb from which the first
practical photovoltaic detector was fabricated in 1955. In 1957,
P. W. Kane, using a method of quantum
perturbation theory (the so-called k·p method), correctly described the
band structure of InSb. Since that time, the Kane band model has been of
considerable importance for narrow-gap semiconductor materials.

The end of the 1950s saw the introduction of narrow-gap semiconductor
alloys in III-V (InAsSb), IV-VI (PbSnTe, PbSnSe), and II-VI (HgCdTe)
material systems. These alloys allowed the bandgap of the semiconductor
and hence the spectral response of the detector to be custom tailored for
specific applications. Discovery of variable bandgap Hg1–xCdxTe (HgCdTe)
ternary alloy in 1959 by Lawson and co-workers triggered an unprecedented degree of freedom in infrared
detector design. Over the next five decades, this material system successfully
fought off major challenges from different material systems, but despite that,
it has more competitors today than ever before. It is interesting, however,
that none of these competitors can compete in terms of fundamental
properties. They may promise to be more manufacturable, but never to
provide higher performance or, with the exception of thermal detectors, to
operate at higher temperature.

Recently, there has been considerable progress towards III-V antimonidebased,
low-dimensional solids development, and device design innovations.
Their development results from two primary motivations: the perceived challenges
of reproducibly fabricating high-operability HgCdTe focal plane arrays
(FPAs) at reasonable cost and theoretical predictions of lower Auger recombination
for type-II superlattice (T2SL) detectors compared to HgCdTe. Lower
Auger recombination translates into a fundamental advantage for T2SL over
HgCdTe in terms of lower dark current and/or higher operating temperature
provided other parameters such as Shockley–Read–Hall lifetimes are equal.

In fact, investigations of antimonide-based materials began at about the
same time as HgCdTe––in the 1950s, and the apparent rapid success of
their technology, especially low-dimensional solids, depends on the previous
five decades of III-V materials and device research. However, the sophisticated
physics associated with the antimonide-based bandgap engineering
concept started at the beginning of the 1990s gave a new impact and interest
in development of infrared detector structures within academic and national
laboratories. In addition, implementation of barriers in photoconductor
structures, in so-called barrier detectors, prevents current flow in the majority
carrier band of a detector’s absorber but allows unimpeded flow in the
minority carrier band. As a result, this concept resurrects the performance
of antimonide-based focal plane arrays and gives a new perspective in their
applications. A new emerging strategy includes antimonide-based T2SLs,
barrier structures such as the nBn detector with lower generation-recombination
leakage mechanisms, photon trapping detectors, and multi-stage/cascade infrared
devices.

This book describes the present status of new concepts of antimonidebased
infrared detectors. The intent is to focus on designs having the largest
impact on the mainstream of infrared detector technologies today. A
secondary aim is to outline the evolution of detector technologies showing
why certain device designs and architectures have emerged recently as
alternative technologies to the HgCdTe ternary alloy. The third goal is to
emphasize the applicability of detectors in the design of FPAs. This is
especially addressed to the InAsSb ternary alloys system and T2SL materials.
It seems to be clear that some of these solutions have emerged as real
competitors of HgCdTe photodetectors. Special efforts are directed on the
physical limits of detector performance and the performance comparison of
antimonide-based detectors with the current stage of HgCdTe photodiodes.
The reader should gain a good understanding of the similarities and
contrasts and the strengths and weaknesses of a multitude of approaches
that have been developed over two last decades as an effort to improve our
ability to sense infrared radiation.

The level of this book is suitable for graduate students in physics and
engineering who have received preparation in modern solid-state physics
and electronic circuits. This book will be of interest to individuals working
with aerospace sensors and systems, remote sensing, thermal imaging, military
imaging, optical telecommunications, infrared spectroscopy, and lidar, as
well. To satisfy all these needs, each chapter first discusses the principles
needed to understand the chapter topic as well as some historical background
before presenting the reader with the most recent information available. For
those currently in the field, this book can be used as a collection of useful data,
as a guide to literature in the field, and as an overview of topics in the field.
The book also could be used as a reference for participants of educational
short courses, such as those organized by SPIE.

The book is divided into ten chapters. The introduction (Chapter 1) gives
a short historical overview of the development of IR detectors with antimonidebased
materials and describes the detector classification and figures of merit of
infrared detectors. The main topics in crystal growth technology, both bulk
materials and epitaxial layers, as well their physical properties are given in
Chapter 2. Special emphasis is paid to the modern epitaxy technologies such
as molecular beam epitaxy and metalorganic chemical vapor deposition.
Chapter 3 provides similar information about type-II superlattices. The next
two chapters concern technology and performance of both bulk as well as
superlattice antimonide-based infrared detectors. New classes of infrared
detectors called barrier detectors, trapping detectors, and cascade detectors
are covered in three succeeding chapters: Chapters 6, 7, and 8. An overview
of antimonide-based FPA architectures is given in Chapter 9. Finally,
remarks are included in the last chapter.